1. Field of the Invention
This invention relates to a signal processing device and a signal processing method and, more particularly, to a signal processing device and a signal processing method which are capable of performing mathematical calculations on a plurality of the signal streams received by a plurality of receiving devices, so as to obtain an additional SNR gain.
2. Description of the Prior Art
Due to weeding out the old and bringing forth the new in various kinds of wireless products, such as cell phones, wireless LANs, GPSs, etc., the requirements of consumers toward these products are turning to low price, diminished size, high performance, etc. However, these requirements make the designs of the wireless products more and more difficult. Take a 2.4 GHz wireless LAN network interface card (802.11n) as an instance, it requires more than two antennas. It is thus a challenge for antenna engineers to arrange two 2.4 GHz antennas in a small region of the wireless LAN network interface card with USB interface.
Recently, with the advancement of computers & network technologies and various kinds of newly developed wireless products such as cell phones, wireless LANs, GPSs, etc., users are used to save and retrieve files among different wireless products. The arising of wireless communication accelerates to establish wireless networks among individual personals, enterprises, and communities.
In general, the wireless network equipment of personal computers includes a computer and a modem which complies with EEE 802.11a/802.11g. An antenna is disposed in or next to the computer, and a RF chip is used for receiving signals via the antenna. An ADC (analog-to-digital convert) is used for converting the received signals to baseband signals. Then, a baseband processing device is used to decode the baseband signals into data. The data may be the files transmitted by another computer of a remote user through wireless network and a transmitter.
There have been many devices and methods which realize the receivers of 802.11a/g modems. However, those prior arts do not fully elaborate the efficiency of the 802.11a/g modems. For example, the maximum transmission rate of the modems is 54 Mbits/sec, but the prior arts usually can not reach the maximum transmission rate owing to the effects of multi-path channels. Actually, it usually succeeds to receive the data only at lower transmission rate under multi-path channel conditions.
In order to improve the receiving performance of high speed wireless transmission, some receivers may adopt multiple antennas. While designing a MIMO (Multiple Input Multiple Output) transceiver, it usually is a challenge to combine the multiple channels. The traditional 802.11g receivers decode both time domain and frequency domain at the same time. That is to say, the traditional 802.11g receivers adopt the CCK (Complementary Code Keying) and OFDM (Orthogonal Frequency Division Multiplexing) at the same time.
In general, the operations such as packet detection and parameter extraction before the data detection can be used for performing the subsequent packet detection and carrier frequency offset acquisition. A conventional way is to adopt the maximum antenna method in which the antenna is used to receive signals with the maximum power. Another conventional way is to simply sum up the received signals of all the antennas.
However, with regard to the former way, not only the intensity of the received signals is limited, but also the advantages of the multiple antennas can not be fully utilized. With regard to the latter way, the antenna may form beams toward the null direction of the incident wave, so as to derive a result just acceptable.
Accordingly, the major object of the inventor is to provide a signal processing device and a signal processing method for performing mathematical calculations on the plurality of the signal streams received by the plurality of receiving devices, so as to obtain an additional SNR gain. Hereby, the processes such as the packet detection, the carrier frequency offset acquisition, etc., can be improved.